This invention relates to headlights of the elliptical type for motor vehicles.
A headlight of the elliptical type consists generally of a reflector having a first focal zone, with a light source placed in the vicinity of the first focal zone, together with a second focal zone. The light from the light source, after being reflected by the reflector, is concentrated in the vicinity of the second focal zone. A lens, which is typically a spherical planar-convex lens, is focussed in the vicinity of the second focal zone and projects the concentrated radiation as a beam on the ground in front of the vehicle, that is to say on the road in normal operation.
It is also conventional to provide in the second focal zone a screen for masking part of the radiation. An upper edge of this screen defines a cut-off line in the formed beam, so that the beam becomes a cut-off or dipped beam, and especially a dipped passing beam.
Although these headlights are very compact, they are particularly sensitive to errors in the positioning of the various optical elements of the headlights themselves. For this reason, modification of the beam by displacement of one of the optical elements is not usually recommended. However, it has been proposed in U. S. Pat. No. 5,707,129, to provide an elliptical headlight in which the reflector and the lamp constitute an assembly which is movable with respect to the lens, this assembly being displaced according to the curvature of a curve in the road, so that it produces a turning beam, that is to say illumination which is adapted to the curve around which the vehicle is travelling.
However, the relative movement of the reflector and lens causes major changes to take place in the optical behaviour of the headlight. These changes are not capable of being easily controlled. In the above mentioned United States patent, it is recommended (and it is in fact necessary) that a masking screen be provided which is movable independently of the assembly consisting of the reflector and the lamp (light source), in order to provide the best possible correction to these optical modifications in the course of the movement.
An object of the invention is to overcome the above mentioned disadvantages, by proposing a headlight of the elliptical type having elements that are movable in order to modify the form of the illuminating beam, while being of less sophisticated construction and giving a beam which is optically defined in the best way.
According to the invention, a headlight for a motor vehicle comprising a light source, a reflector with two focal regions, and a lens, the source being located in one of the two focal regions in such a way as to produce a pool of reflected light in the other focal region, and the lens being arranged to convert this pool into a beam projected on the road, is characterised in that the headlight further includes means for selectively moving (displacing) the source with respect to the reflector.
The invention leads to the surprising result that a small displacement of the light source enables various beam configurations to be obtained. These configurations are for example: (a) a dipped passing beam of the type known to be best for town driving; or (b) a dipped passing beam adapted so that it is particularly suited to driving on a trunk road (variously referred to as a motorway, thruway or autoroute, for example); or (c) a dipped turning beam, as discussed above; or (d) a beam which is adapted to prevent drivers travelling in the opposite direction from being dazzled by the effects of mud on the headlight, which causes scattering of the light beam.
According to various preferred but optional features which may be taken singly or in any practical combination:
the means for displacing the source (such as a lamp) with respect to the reflector comprise a lamp base or lamp holder, and means for holding the said base while enabling the latter to be displaced within the headlight;
the means for selectively displacing the source with respect to the reflector are arranged to shift the lamp through one or a few millimeters horizontally towards one side of the reflector;
the means for selectively displacing the source with respect to the reflector are arranged to permit such relative movement in a vertical direction;
the headlight includes means for driving the source with respect to the reflector into two distinct positions, one of which corresponds to a first dipped passing beam having a first zone of concentration of light intensity which is substantially centred in front of the vehicle, while the other said position corresponds to a dipped passing beam having a second zone of concentration of light intensity which is offset substantially horizontally towards one side with respect to the concentration zone of the first dipped beam;
the headlight includes means for driving the source into two distinct positions, one of which corresponds to a first dipped passing beam having a first zone of concentration of light intensity which is substantially centred in front of the vehicle, while the other said position corresponds to a dipped passing beam having a second zone of concentration of light intensity which is offset to the left of the concentration zone of the first dipped beam;
the means for selectively displacing the source with respect to the reflector are arranged to give three relative positions of the source and reflector, which are distinct and which correspond to three distinct dipped passing beams, namely a first beam with a centred light concentration zone, and two further beams, each having a light concentration zone offset in a direction which is different with respect to the concentration zone of the first beam;
the headlight includes means for displacing the light source, on command, by one or more millimeters with respect to the reflector in a leftward or rightward or downward direction with respect to the direction of propagation of the light;
the means for displacing the source with respect to the reflector are arranged to displace the source selectively in each of the directions consisting of leftward, rightward and downward;
the means for selectively displacing the source with respect to the reflector are arranged to produce, on command, relative displacement such as to provide selectively a left or right offset of the source, the value of which is so chosen as to give a dipped turning beam, on the left or right respectively.